Recently, the integration level and speed of integrated circuits have been more improved, and it is required to produce a direct-current power supply capable of supplying high current exceeding 30 amperes with low voltage about 1 Volt. Generally, a switching power supply is used as a direct-current power supply for generating high current with low voltage.
As an example of the switching power supply, there is a direct current voltage converter (DC-DC converter) which obtains a rectangular wave output by repeating on/off operation by a switch element such as a field effect transistor, and obtains direct-current power supply by smoothing the rectangular wave output by a lowpass filter formed of an inductor and a capacitor.